During the manufacture of integrated circuits (ICs) containing more than one layer of poly-silicon (or poly-silicon features created from poly-silicon layers deposited at different times), it is not uncommon to encounter the formation of stringers. Stringers can be broadly defined as residual materials left over from an etch process. Such stringers can present problems when they are composed of conductive materials (e.g., poly-silicon), because they can provide conductive paths between adjacent features, resulting in short circuits.
In the past, IC manufacturers have sought to remove poly-silicon stringers using isotropic etchants such as NF3 and SF6. Such techniques may be useful for ICs that have critical dimensions of above approximately 0.35 microns, however, as these critical dimensions shrink (e.g., to on the order of less than 0.35 microns and smaller), the use of isotropic etchants must be avoided so as not to undercut useful device features (e.g., gate structures and the like). As a result, others have attempted to remove stringers by adding dielectric spacer layers or even changing the shape of underlying structures (e.g., so as to provide a more uniform etch surface). These solutions involve complex manufacturing processes that deviate from the goal of simplifying the manufacture of ICs whenever possible. Still others have suggested that dummy features could be introduced on areas of a semiconductor die to create diversionary paths for the short circuits that might result from the presence of stringers. The problem with this solution is that it tends to waste valuable die space.
Accordingly, it would be useful to have a procedure for producing stringer-free poly-silicon layers that avoids the drawbacks of prior solutions.